Chair base



FIG. 1 is a perspective view of a chair base embodying the new design.

FIG. 2 is a left side view thereof, the right side view being a mirror image of the left side view.

FIG. 3 is a front elevational view thereof.

FIG. 4 is a rear elevational view thereof.

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The broken lines showing of the chair seat and backrest are included for the purpose of illustrating environmental structure and form no part of the claimed design. 

CLAIM The ornamental design for a chair base, as shown and described. 